1. Field of the Invention
The present invention relates to display devices, and more particularly, to frame synchronization methods and devices.
2. Description of the Prior Art
When a frame rate of input frames differs from a frame rate of output frames, or when input frames of two paths having different frame rates respectively should be outputted with a common frame rate, frame rate conversion is required. Normally in a monitor, a frame rate conversion method for performing the frame rate conversion mentioned above needs a frame buffer for temporarily storing frame data, and then an image processor performs image processing of the frame data.
According to the prior art, however, some problems typically occur during the frame rate conversion as described in the following.
One problem is the frame-tear problem, which means within frames displayed on the monitor, a portion of the displayed frames and another portion of the displayed frames respectively correspond to different frames of different time points. The frame-tear problem occurs because during a reading operation of frame data temporarily stored in the frame buffer, the image processor first continuously reads a certain frame's data and then starts reading the next frame's data even if the next frame's data has not been stored in the frame buffer to replace the original frame data.
Another problem is a side effect of increasing the number of the frame buffer (e.g. two frame buffers corresponding to an input frame) to provide enough space for storing frame data and solving the above-mentioned frame-tear problem. The side effect of this revised frame rate conversion method is that when a frame rate of output frames is greater than a frame rate of input frames, some of the output frames should be outputted repeatedly. Conversely, when a frame rate of output frames is less than a frame rate of input frames, some of the output frames should be omitted. As a result, a video object (e.g. text) in a scrolling banner displayed on a monitor utilizing this method will appear to be moving at an unsteady speed. Furthermore, an additional material cost is required to implement this architecture since the volume of the frame buffer is increased.
Another method utilizes line buffers together with related control circuits to synchronize frame rates of input and output frames. This frame synchronization method has some implementation limitations.
One implementation limitation is that utilizing the related control circuits to control data synchronization is required, so as to prevent the line buffers from having problems such as data overflow or data underflow.
Another implementation limitation is that the format of the output video signal should approach a specific requirement since digital display devices from different manufacturers, for example, panels, have various requirements for the acceptable video signal format thereof, which may differ from manufacturer to manufacturer. If the output video signal does not meet the specific requirement of the panel (e.g. the pixel numbers of all horizontal lines are completely the same), it will not satisfy the requirements of all panels regarding the outputted format. As a result, the digital display device(s) (e.g. one of the panels) may not accept that the output video signal fails to meet the digital display device's requirements for the video signal format, and therefore, may not be able to display the video signal.
Therefore, on one hand, although the conventional frame rate conversion method may adjust the frame rate during displaying, the unsteady moving speed problem exists. On the other hand, although the conventional frame synchronization method mentioned above may solve the unsteady moving speed problem, the conventional frame synchronization method is not able to change the frame rate during displaying. As a result, no matter which method is utilized for display control of the monitor displaying the frames, at least one problem exists. Therefore, to a user viewing the displayed frames, the displayed frames are quite unsteady.